A desirable property of powder coating compositions is that they maintain suitable flow out and cure characteristics during application to a substrate. Typically, a powder coating composition which is applied to a surface heated, and melts, experiences a reduction in viscosity, and flows out onto its substrate. If the viscosity of the powder coating melt remains sufficiently low for a sufficient time, then volatile byproducts in the coating can escape. Continued heating of the powder coating begins crosslinking with the consequence that the viscosity increases and any remaining defects are trapped in the coating.
The use of solid glycoluril type amino resin crosslinkers are generally advantageous in powder coating compositions. However, volatile byproducts, such as methanol are evolved during cure. It is important that improved formulations be developed which provide opportunity for such glycoluril amino resin byproducts to escape during the coating process to give coatings of improved appearance and thickness.
Glycoluril resin type amino crosslinking systems such as those containing tetramethoxymethyl glycoluril may produce pinholes in thicker films (over about 89 microns due to methanol outgassing. It has now been discovered that addition of suitable rheology control additives allows for the production of defect free films thicknesses in excess of 115 microns.